Microtubule organization in Xenopus eggs during the first cleavage and its role in cytokinesis

It has been suggested that the organization of microtubules during mitosis plays an important role in cytokinesis in animal cells. We studied the organization of microtubules during the first cleavage and its role in cytokinesis of Xenopus eggs. First, we examined the immunofluorescent localization of microtubules in Xenopus eggs at various stages during the first cleavage. The astral microtubules that extend from each of the two centrosomes towards the division plane meet and connect with each other at the division plane as cytokinesis proceeds. The microtubular connection thus advances from the animal pole to the vegetal pole, and its leading edge is located approximately beneath the leading edge of the cleavage furrow. Furthermore, an experiment using nocodazole suggests that microtubules have an essential role in advancement of the cleavage furrow, but neither in contraction nor maintenance of the already formed contractile ring which underlies the cleavage furrow membrane. These results suggest that the astral microtubules play an important role in controlling the formation of the contractile ring in Xenopus eggs.